FWIW, coastal Democrats are equally offended with being lumped in with Trump supporters, Scots would probably be equally offended with being lumped in with English, and Croatians would be equally offended with being lumped in with Yugoslavians, so at least I'm an equal-opportunity offender.
Before the breakup of Yugoslavia, some people identified as yugoslavian, yes - as one might identify as European today, but by far the majority of population identified as being one of yugoslavia's constituent ethnicities. After the breakup of Yugoslavia, practically nobody identifies as yugoslavian today - what would be the point, since that attempt at unification seems definitively dead to history now?
I assume you meant "lumped with Serbs (as being Yugoslavian)?".
Many people in central Bosnia identified as Yugoslavians before the war and I would say most in the same region born in late 60s, 70s would have identified the same. So when someone says Yugoslavia, I think Sarajevo and Bosnia, not Serbia.
So by the end of yugoslavia, got relatively substantial but still by far the majority always identified with some specific ethnicity.
Now I presumed most people revised their identification in 90' for political reasons/safety, but could be emigration as you say played a significant role too, especially in bosnia.
And yeah, a fair proportion would prob be offended by an imputation of yugoslavian identity today, because of the ethnically divided politics.
But I think further than that, a significant chunk of the people not too happy that yugoslavia failed and disintegrated (such as myself and I believe many left-leaning people around) still can't see much sense in identifying as being ethnically yugoslavian. Yugoslavia is no more; yugoslavian identity was a composite one in its rather recent origin; people knew specific ethnicities of their parents and choose to think of themselves as yugoslavian first, or interpreted having parents of different ethnicities as being that identity. As a political project - and it was that - it died just by the time it was getting any substantial traction, so seems rather pointless today.